The invention relates to control means for a machine structure oscillatingly supported on a base unit about an axis of rotation of an agricultural machine.
In the following specification, the invention is described in connection with a cutter table oscillatingly secured to a harvester thresher as representing all such machine structures such as cutters, mowers or other harvesting machines.
In the operation of a harvester thresher, the cutter table of this machine has, in many cases, so to be guided over the ground that it does not dig into the ground, on the other hand, however, rests with such a residual weight on the ground that it does not lift up in case of ground unevennesses but rather follows these ground unevennesses and cuts the wheat at a uniform height.
In order to determine the residual weight, the cutter tables are supported via springs relative to the undercarriage.
In the past, the cutter table was, in most cases, rigidly secured to the conveyor channel at right angles relative to the longitudinal direction and hence in parallel to the transverse axis of the harvester thresher. For lifting or lowering the cutter table, the conveyor channel was rotated about its transverse axis.
During operation for instance on a side slope when using very broad cutter tables, it can happen that the table digs into the ground of the lower side of the slope because the heavy harvester thresher sinks deeper into the ground with its wheels on the lower side of the slope than on the slope upper side. The machine is thus, with its transverse axis, no longer in parallel to the slope position of the ground. The cutter table which is often double as broad as the machine, subsequently, is no-longer in a ground-parallel inclination either unless it can slue or oscillate about the longitudinal axis of the harvester thresher. On the lower side of the slope it will dig into the ground and on the upper side of the slope it is guided with a distance above the ground.
There are slope equalizing systems on the market which adjust the inclination of the cutter table. Such systems are designed as a freely sluing or oscillating system, wherein the cutter table is kept at optimum inclination by the ground contact pressure or is kept in position by means of power-operated swiveling devices.
Such devices may be provided directly at the conveyor channel and the cutter table may also be part of a two-part adapter, one part of which is assigned to the conveyor channel and the second part of which to the cutter table. The operation of the oscillating device is such that one adapter part can be tilted relative to the second adapter part. Such an adapter oscillator device has the advantage that constructionally neither the conveyor channel nor the cutter table, designed as if no oscillator device was provided, need be altered.
The free oscillation of the cutter table has the advantage that it is the ground contact of the cutter table which determines optimum inclination. Such systems have for instance been known from German Offenlegungsschrift and GDR Patent Specification No. 94,725.
The majority of cutter tables however have so been designed that they are imbalanced relative to the transverse center, since the weight of the drives for cutter knives, draw-in worm and winch has in most cases been provided on one and the same side of the cutter table. In case of free oscillation about a center axis, the cutter table inclines to the heavier side. The operation of the free oscillation is thereby substantially disturbed.
In order to bring about the balance, additional weights have been provided on the lighter side; it is however not of advantage to additionally increase the weight of the cutter table which is per se heavy.
In accordance with German Offenlegungsschrift 35 44 918, a spring mechanism has been described for the provision of the balance of an unbalanced cutter table wherein, via an angle lever, a roller support is obtained on the bracket of the conveyor channel, the roller support being spring-loaded.
Such sophisticated structure is in the first instance very much endangered by damages when the cutter table is coupled in and in the second instance it has to be correspondingly biased in each coupling operation in order to have the spring force available over the total oscillation range.
A similar operation has been described in German Patent Specification No. 2,208,243. But in this case, too, the big disadvantage is to be seen in that when coupling on or off, the balancing spring has either to bias itself, or relax, respectively, or has to be relaxed manually prior to coupling off and biased manually after coupling on. If the spring is automatically biased or relaxed in the coupling operation, there is a substantial danger of accidents since the cutter table has the tendency of adjusting itself about half of the oscillation path at right angles relative to the conveyor channel before it is completely coupled on or off. This effect is produced in that the spring, caused by the spring force varying as a function of the path, does not act uniformly over the whole oscillation path.
When the cutter table is lifted, it is of importance and desirable that the cutter table will swing into its position parallel to the harvester thresher. But it is exactly in this desired smooth oscillation that the problem comes up that without employing corresponding means which lock the oscillation as soon as the table is lifted, the cutter table will move to both sides. This may occur by vibrations of the machine caused by uneven ground but also simply by a variable feeding of the table with the harvested material.
In GDR Patent Specification No. 94,725, German Patent Specifications No. 2,133,746 and No. 2,208,243, stabilizer springs have therefore been described which draw, or press, respectively, an oscillatingly inclined cutter table into the parallel again as soon as the table is taken off ground contact. These springs, however, have to be biased during the oscillation operation and hence impair the desired easy motion of the oscillation movement when copying the ground contour. The ground contact pressure required for guiding the table according to the ground contour has to be selected higher and the resulting disadvantages have to be accepted.
Controlled oscillation is performed by one or two hydraulic cylinders. This can be accomplished by manual control of the hydraulic cylinders or by means of sensors provided on the cutter table trough continuously scanning the distance to the ground and transmitting corresponding control signals to the control valve for the hydraulic cylinder, or hydraulic cylinders. In case of manual control, the problem is that the operator is not aware of the inclination of the table particularly in case of reduced vision because of dust and darkness. The result in many cases is that a substantially different stubble height corresponding to the cutter table width is obtained. This again is of disadvantage for the subsequent treatment of the stubbles.
Sensors, scanners and similar devices detecting the ground contour have the big disadvantage that, in the first instance, they can be provided only too far behind the cutter line and they operate effectively only when the cutter bar has already passed the changed ground contour, and that they cannot, secondly, differentiate between genuine and non-genuine obstacles. A pile of straw or loose earth should not make it react, a heavy stone, for instance should cause the cutter table to oscillate effectively.
The mentioned free oscillation according to the ground contour by the weight of the cutter table supported on the ground is to be preferred in automatic guiding. The two outer shoes which generally extend beyond the front of the cutter line of the cutter table will be sufficient to effect, by their support force on the ground, the oscillation movement of the cutter table. If the position of the cutter table is higher, on the other hand, it is also desirable to readjust the inclination by manual control.
In both cases, however, the cutter table should automatically find its position parallel to the transverse axis of the harvester thresher, if the operator so wishes.